JP5313456B2 - Surface protection film - Google Patents

Description

  The present invention relates to a surface protective film based on a polyester film. More specifically, the present invention relates to a surface protective film that is excellent in transparency, has little charge when being rubbed or peeled, and is easy to wipe off sticky foreign substances adhering to a surface layer.

  Conventional surface processing of word processing, various displays such as computers and televisions, or optical sheet components such as polarizing plates, retardation plates, viewing angle control sheets, and laminates based thereon, polyethylene, polypropylene, polyester, etc. for the purpose of surface protection A transparent protective film is laminated. In particular, the polarizing plate is wound up in a roll state from the manufacturing process of the polarizing plate to being incorporated into a liquid crystal display or the like, unrolled again, laminated with a sheet coated with an adhesive on the release film, and wound up again and again. Or it cuts to a desired size as it is. The cut polarizing plates are stacked, packed and shipped. In the liquid crystal display manufacturing process, the stacked polarizing plates are picked up one by one and used. In these manufacturing processes, there is a problem that surrounding dust is caught due to frictional charging with the conveying roll or peeling charging when picking up one sheet at a time.

On the other hand, in recent years, for large monitors and television displays, there is a process of washing the liquid crystal display whose surface is protected with a surface protection film with water before connecting the drive parts, and the surface dust is carefully removed. After that, it is sent to the defect inspection process. Therefore, the surface layer of the film is required to have an antistatic property and no difference in color due to scratches, coating film dropping or discoloration in the surface layer itself in the water washing step.
JP 11-256116 A

  The present invention has been made in view of the above-described background art, and its purpose is to provide excellent anti-friction charging and peeling charging when used for surface protection of various optical sheets, particularly various optical sheets for large-area large displays. Another object of the present invention is to provide a surface protective film which has an effect of prevention and is excellent in water resistance of a surface layer which is less likely to be damaged even when the surface protective optical sheet is subjected to defect inspection after washing with water.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor has developed an aqueous coating liquid containing a specific resin component, an antistatic agent and an antifouling agent on one surface, and containing a specific water affinity liquid. The surface layer formed by using it was found to have excellent antistatic properties and good water resistance, and as a result of further studies, the present invention was reached.

  Thus, according to the present invention, “a surface protective film having a surface layer formed from a coating liquid having the following composition on one side of a polyester film and an adhesive layer on the other side, the surface layer having a boiling point of 150 ° C. or higher. A surface protective film formed by using an aqueous coating solution containing 0.2 to 3.0% by weight of a water-soluble or water-miscible liquid based on the total weight of the solvent in the coating solution " Is done.

（式中、Ｒ^１およびＲ^２は、相互に独立して水素または炭素数１〜４のアルキル基を表すか、あるいは一緒になって任意に置換されてもよい炭素数１〜１２のアルキレン基を表す）
（Ｃ）ポリビニルアルコールまたはポリエチレンイミンを塩素化アルキロイルまたはアルキルイソシアネートで長鎖アルキル化した共重合体からなる防汚剤：塗液中の有効成分（溶剤を除いた成分）重量を基準として４〜９重量％ Composition of coating liquid (A) a polyester resin, an acrylic resin, at least one resin component selected from the group of acrylic modified polyester resin and urethane resin (component excluding the solvent agent) active ingredient in the coating solution by weight 55 to 89% by weight,
(B) a polythiophene-based conductive a polymer antistatic agent whose main recurring unit a unit represented by the following general formula: 7-40 weight (components excluding the solvent agent) by weight active ingredient in the coating solution as a reference %,

(In the formula, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms, or together, the alkylene group having 1 to 12 carbon atoms which may be optionally substituted together) Represents
(C) a polyvinyl alcohol or polyethyleneimine chlorinated alkyloyl or alkyl isocyanate composed of a copolymer which is a long chain alkylating antifouling agent (component excluding the solvent agent) active ingredient in the coating liquid 4, based on the weight 9% by weight

Moreover, as a preferable aspect,
The surface resistivity of the surface layer is 1 × 10 ⁵ to 1 × 10 ¹² Ω / □,
The water contact angle of the surface layer is 70 ° to 100 °,
-The peel strength of the surface layer with respect to the acrylic adhesive tape is 2-6 N / 25 mm or more,
-Having a primer layer formed from a coating solution containing a silane coupling agent as a main component between the polyester film and the surface layer;
-The surface protection film which comprises at least 1 requirement that the adhesive force of an adhesive layer is 0.03-0.50N / 25mm is provided.

  Since the surface protective film of the present invention has a surface layer formed from a specific coating liquid on one side surface of the polyester film, it has excellent peeling antistatic effect and water resistance. Therefore, for example, when used in an optical sheet manufacturing process such as a polarizing plate, a retardation plate, a viewing angle widening film, or a panel manufacturing process using these optical sheets, the surface of the optical sheet is charged by friction or peeling in each process. In addition, the surface layer is not scraped or discolored even after the water washing step. For example, if it is used for a surface protective film of a polarizing plate, a defect inspection of a product can be accurately performed.

Hereinafter, the present invention will be described in detail.
The surface protective film of the present invention comprises at least one resin component selected from the group consisting of polyester resin, acrylic resin, acrylic-modified polyester resin and urethane resin, an antistatic agent and an antifouling agent on one side of the polyester film. It is necessary to have a surface layer formed from the coating liquid containing and to have an adhesive layer on the other surface.

  The resin component used here preferably has a secondary transition temperature in the range of 20 to 150 ° C. When this temperature is less than 20 ° C, the blocking resistance of the surface layer tends to deteriorate, and conversely, when it exceeds 150 ° C, the abrasion resistance of the surface layer coating film tends to be insufficient.

  As the polyester resin preferably used, as dicarboxylic acid components, for example, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hexahydroterephthalic acid, 4.4'-diphenyldicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid Acid, 5-Na sulfoisophthalic acid, 5-K sulfoisophthalic acid and the like, and glycol components such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, cyclohexanedimethanol, Polyesters using polyethylene glycol, bisphenol A / alkylene oxide adducts and the like can be mentioned, and among them, copolymer polyesters containing these components are preferred. In addition, the polyester resin whose secondary transition temperature is 20 to 150 ° C. is obtained by using an aromatic dicarboxylic acid as a main component as a dicarboxylic acid component and appropriately selecting and combining the glycol component so that the secondary transition temperature is in the above range. Can be easily obtained.

  Such a polyester resin can be produced by a conventional method, and its weight average molecular weight is preferably in the range of 10,000 to 50,000 from the viewpoint of abrasion resistance and blocking resistance of the surface layer coating film.

  Next, as an acrylic resin which is preferably used, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, ethyl crotonate, glycidyl methacrylate, -2-hydroxy acrylate Mention may be made of copolymers containing acrylate monomers such as ethyl and 2-ethylhexyl acrylate.

  This acrylic resin includes, in addition to at least one of the above acrylate monomers, acrylamide, methacrylamide, acrylic acid, methacrylic acid, sodium acrylate, potassium methacrylate, ammonium acrylate, N-methylolacrylamide, Other acrylic monomers such as N-methoxymethylacrylamide may be included as a copolymerization component, and other than acrylics such as vinyl chloride, vinyl acetate, styrene, vinyl ether, butadiene, isoprene, sodium vinyl sulfonate, etc. These monomers may be included as a copolymerization component.

  The acrylic resin contains a hydrophilic monomer such as acrylate, methacrylate, acrylic acid, acrylamide, 2-hydroxyethyl acrylate, N-methylolacrylamide as a copolymer component, When the surface layer coating liquid is an aqueous coating liquid, it is preferable because dispersibility and solubility are improved. Moreover, the copolymer which introduce | transduced various functional groups into the molecular side chain of an acrylic resin may be sufficient.

Acrylic resins with a secondary transition temperature of 20 to 150 ° C. use a hard component such as methyl methacrylate or ethyl methacrylate as a main component, and a soft component such as an acrylate ester as a copolymer component. It can be obtained by copolymerizing at a rate at which the temperature falls within the above range. Furthermore, the secondary transition temperature of the acrylic resin can be adjusted by using a component having a methylol group or a methoxymethyl group as a copolymerization component and crosslinking these groups.
The weight average molecular weight of the acrylic resin is preferably in the range of 10,000 to 500,000 from the viewpoint of abrasion resistance and blocking resistance of the surface layer coating film.

  Next, as an acrylic modified polyester resin (hereinafter, simply referred to as a modified polyester resin) that is preferably used, the above-mentioned polyester resin and the above-mentioned acrylate-based monomer and / or other acrylic-based monomer are used. And a modified polyester resin having a secondary transition temperature of 20 to 150 ° C. obtained by polymerizing the above. Such a modified polyester resin is obtained, for example, by graft polymerization of the above acrylate monomer and / or other acrylic monomer to a polyester resin in an aqueous liquid using a radical polymerization initiator. Can do. This modified polyester resin may have a functional group in the molecular side chain. Moreover, it is preferable that the weight average molecular weight of a modified polyester resin is the range of 10,000-500,000 from the point of the abrasion resistance and blocking resistance of a surface layer coating film.

  The acrylic modified polyester resin having a secondary transition temperature of 20 to 150 ° C. uses a copolymer polyester resin having a secondary transition temperature of 20 to 150 ° C., and a hard component such as methyl methacrylate or ethyl methacrylate and acrylic acid. It can be obtained by graft copolymerizing a soft component such as an ester at a ratio at which the secondary transition temperature of the resulting acrylic-modified polyester resin is 20 to 150 ° C.

  Next, as a polyurethane resin preferably used, for example, a polyurethane resin having a secondary transition temperature of 20 to 150 ° C. produced from aliphatic polyether, aliphatic polyester, diisocyanate, diamine, glycol, dimethylolpropionate, etc. Can give. The weight average molecular weight of the polyurethane resin is preferably in the range of 5,000 to 50,000 from the viewpoint of abrasion resistance and blocking resistance of the surface layer coating film.

  Note that the polyurethane resin having a secondary transition temperature of 20 to 150 ° C. is obtained by appropriately adding an aromatic component to the polyether or polyester, using an aromatic diisocyanate, diisocyanate, alkylene diamine, alkylene glycol, dimethylol propionic acid. It can be easily obtained by controlling the amount of salt used.

  The resin component demonstrated above may be used individually, respectively, or 2 or more types may be mixed and used for it. Such a resin component is preferably used in the form of water or an aqueous dispersion dispersed in a solution containing water as a main component or a water-solubilized aqueous solution from the viewpoint of handleability. In addition, in order to improve the water resistance and blocking resistance of the resulting surface layer coating film, it is selected from methylolated or alkylolized melamine-based, urea-based, glyoxal-based, acrylamide-based compounds, epoxy compounds, and polyisocyanates. Further, at least one kind of crosslinking agent may be contained.

  The antistatic agent used in the surface layer of the present invention is derived from a polythiophene-based conductive polymer whose main repeating unit is a unit represented by the following general formula, particularly a polysulfonic acid whose counter anion contains styrenesulfonic acid as a copolymerization component. Preferred is a conductive polymer that is a polyanion formed.

（式中、Ｒ^１およびＲ^２は、相互に独立して水素または炭素数１〜４のアルキル基を表すか、あるいは一緒になって任意に置換されてもよい炭素数１〜１２のアルキレン基を表す）

(In the formula, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms, or together, the alkylene group having 1 to 12 carbon atoms which may be optionally substituted together) Represents

  Examples of the polythiophene-based conductive polymer (a complex of polycationic polythiophene and anion) preferably used include polythiophene used as an antistatic layer described in JP-A-2005-88389, JP-A-2006- Polythiophene described in Japanese Patent No. 294532 can be mentioned. Specifically, for example, poly (3,4-ethylenedioxythiophene) [about 1/3 of the thiophene ring is cationized] and polystyrene A complex with sulfonic acid (about half of the sulfonic acid is anionized) can be mentioned.

  As the antifouling agent used in the surface layer of the present invention, a polymer having a long alkyl side chain, for example, polyvinyl alcohol or polyethyleneimine having an alkyl side chain having 12 or more carbon atoms, particularly 16 to 20 carbon atoms, is chlorinated alkyloyl or A long-chain alkylated polymer with an alkyl isocyanate is used. Specific examples include polyvinyl-N-octadecyl carbamate obtained by the reaction of polyvinyl alcohol and octadecyl isocyanate, and polyethylene imine-N-octadecyl carbamate obtained by the reaction of polyethylene imine and octadecyl isocyanate.

  Since these antifouling agents are mixed with the aforementioned resin component and antistatic agent, it is preferable to use water or those dispersed in a solvent containing water as a main solvent. Specific examples include Pyroyl 406 manufactured by Yushi Co., Ltd., PX-RP10W manufactured by Nippon Shokubai Co., Ltd., and Resam M-643 manufactured by Chukyo Yushi Co., Ltd.

  In the present invention, within the range not impairing the object of the present invention, for example, within the range not impairing the transparency, other antifouling agents such as silicone-based release agents, fluorine-based release agents, paraffin wax, Carnauba wax or the like may be used in combination.

  The content ratio of the components described above in the coating liquid is 55 to 90% by weight, preferably 70 to 90% by weight of the resin component based on the weight of the active ingredient in the coating liquid (a component excluding a solvent such as water). The antistatic agent is contained in an amount of 7 to 40% by weight, preferably 10 to 25% by weight, and the antifouling agent is contained in a proportion of 3 to 12% by weight, preferably 4 to 9% by weight, preferably the above resin component, antistatic agent and The total amount of the antifouling agent needs to be 100% by weight, and the surface layer is a water-soluble or water-miscible liquid having a boiling point of 150 ° C. or higher in the coating liquid based on the total weight of the solvent. It must be prepared using an aqueous coating solution containing 2 to 3.0% by weight.

  Here, when the ratio between the antistatic agent and the resin component is within the above range, the adhesion between the polyester film and the surface layer is good, and the water resistance and the abrasion resistance of the surface layer are good. It becomes.

  Further, when the ratio of the antifouling agent is within the above range, foreign substances such as adhesive substances are easily removed from the surface of the surface protective layer, so that the brushing at the time of water washing is shortened in time. Moreover, it can be performed weakly in strength, and further, the removability when water remaining on the surface after cleaning is blown off with clean air is improved. On the other hand, the surface protective film of the present invention is finally peeled and removed from the surface of the optical sheet such as a polarizing plate. In the step of peeling and removing the surface protective film, the adhesive tape or the adhesive roll is removed from the surface of the surface protective film. The surface protective film is peeled off from the optical sheet or the like by pasting to the optical sheet. Therefore, when the content of the antifouling agent exceeds 12% by weight, the releasability becomes too strong (peeling strength becomes too light), and the pressure-sensitive adhesive tape or pressure roll used for peeling and removal and the surface protective film Adhesion with the surface layer becomes weak, and the surface protection film cannot be peeled off from the optical sheet such as polarized light. When the physical properties of these surface layers are defined by the contact angle of water, the range of 70 ° C. to 100 ° is preferable, and when defined by the peel strength with the acrylic adhesive tape 31B manufactured by Nitto Denko Corporation, the range of 2 to 6 N / 25 mm is preferable.

Furthermore, the surface layer of the present invention preferably has a surface resistivity of 1 × 10 ⁵ to 1 × 10 ¹² Ω / □. If this value is less than 1 × 10 ⁵ Ω / □, the antistatic layer becomes fragile, which is not preferable. Conversely, if it exceeds 1 × 10 ¹² Ω / □, the antistatic property is insufficient.

  Next, examples of the water-soluble or water-miscible liquid having a boiling point of 150 ° C. or higher that are blended in the coating liquid for forming the surface layer include glycerin, dimethyl sulfoxide, diethylene glycol, diethylene glycol dimethyl ether, and diethylene glycol diethyl ether. , Diethylene glycol di-n-propyl ether, diethylene glycol di-n-butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, diethylene glycol mono Ethyl ether acetate, diethylene glycol acetate mono-n-butyl ether, 1-methyl And the like can be mentioned-2-pyrrolidone, boiling point is not limited thereto as long as a liquid having a water-soluble or water-miscible at 0.99 ° C. or higher.

In the present invention, at least one kind of a water-soluble or water-miscible liquid having a boiling point of 150 ° C. or higher is contained in an amount of 0.2 to 3.0% by weight based on the solvent weight in the coating liquid. There is a need. When the content of the liquid having a boiling point of 150 ° C. or more and water-soluble or water-miscible is less than 0.2% by weight, a sufficient surface resistivity can be obtained even if the antistatic agent is contained in the above range. It becomes difficult to obtain. On the other hand, if the content of this liquid exceeds 3.0% by weight, not only the effect will not increase, but also the solvent cost will increase or the evaporation rate of the solvent will slow down and it will be necessary to lower the coating speed. This causes problems such as lowering.
The thickness of the surface layer is preferably in the range of 0.02 to 0.20 μm, more preferably in the range of 0.03 to 0.10 μm.

  In addition to the above components, the coating liquid for forming the surface layer of the present invention has an average particle size of 0.01 to 0 as a lubricant in order to improve the slipperiness and blocking resistance of the coating film. .5 μm of inorganic or organic fine particles can be contained, for example, in a proportion of 0.001 to 5% by weight. Specific examples of such fine particles include inorganic fine particles such as silica and kaolin, polystyrene resin, crosslinked polystyrene resin, acrylic resin, crosslinked acrylic resin, melamine resin particles, silicone resin, fluorine resin, urea resin, benzoguanamine resin, and the like. Can give. The organic fine particle may be a thermoplastic resin or a thermosetting resin as long as it is a resin that can maintain the fine particle state in the coating film, and has been crosslinked with a degree of crosslinking depending on the purpose. Resin may be used.

  Further, as the cross-linking agent, at least one cross-linking agent selected from methylolated or alkylolized melamine-based, urea-based, glyoxal-based, acrylamide-based compounds, epoxy compounds, and polyisocyanates can be contained. However, if the content of the crosslinking agent is too large, the coating film may become brittle.

  Any conventionally known application method can be adopted as a method for applying the coating liquid onto the polyester film surface. For example, a roll coating method, a gravure coating method, a micro gravure coating method, a reverse coating method, a roll brush method, a spray coating method, an air knife coating method, an impregnation method, a curtain coating method, etc. may be applied alone or in combination. A slight amount of an organic solvent or a surfactant may be included for the purpose of assisting the stability of the coating appearance such as repelling.

  The surface protective film of this invention provides an adhesive layer in the surface on the opposite side to the surface which provides the surface layer demonstrated above. Furthermore, a release (release) film treated with a release agent may be bonded to the surface of the pressure-sensitive adhesive layer as necessary.

  As the pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer, an acrylic, rubber-based or urethane-based pressure-sensitive adhesive can be used, and an acrylic pressure-sensitive adhesive is particularly preferable from the viewpoint of durability of the pressure-sensitive adhesive layer. In addition, it is important that the adhesive layer has no transfer of the adhesive to the other side when it is peeled again after the release film is bonded, and the adhesive force of the adhesive layer is 3 to 50 g in order to satisfy such requirements. / 25 mm is preferable.

  The pressure-sensitive adhesive type may be any of thermosetting type, UV (ultraviolet) curing type, EB (electron beam) curing type, and hot melt type. From the viewpoint of suppressing the above, an isocyanate-based or epoxy-based crosslinking agent may be appropriately used.

  The adhesive strength of the pressure-sensitive adhesive layer is expressed as a force when the surface of the pressure-sensitive adhesive layer is bonded to a stainless steel plate (SUS304) and peeled at an angle of 180 ° at a speed of 300 mm / min after 1 day at 23 ° C.

  The application method of the pressure-sensitive adhesive layer can also adopt any method similar to the application method of the surface layer described above, for example, roll coating method, gravure coating method, micro gravure coating method, reverse coating method, roll brush method, A spray coating method, an air knife coating method, an impregnation method, a curtain coating method, a die coating method, a doctor blade coating method, or the like may be applied alone or in combination.

  The thickness of the pressure-sensitive adhesive layer is preferably in the range of 3 to 100 μm, particularly 5 to 50 μm. When the thickness is less than 3 μm, a sufficient adhesive effect may not be obtained, while when it exceeds 100 μm, the quality is excessive and uneconomical.

  The polyester film on which the surface layer and the pressure-sensitive adhesive layer are formed is a film made of polyester formed from the following dicarboxylic acid component and glycol component.

  Examples of the dicarboxylic acid component preferably used include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, hexahydroterephthalic acid, 4.4'-diphenyldicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid and the like. Among them, terephthalic acid or 2,6-naphthalenedicarboxylic acid is preferable from the viewpoint of the mechanical properties of the film.

  Examples of the glycol component include ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, polyethylene glycol and the like. Among them, ethylene glycol is preferable from the viewpoint of the mechanical properties of the film.

Such a polyester may be a copolyester obtained by copolymerizing the above dicarboxylic acid component or glycol component as the third component, and the resulting polyester is substantially linear. It may be a polyester copolymerized within a range (for example, 5 mol% or less).
Of these, polyethylene terephthalate or polyethylene-2,6-naphthalate is preferable.

  Such a polyester can be produced by a conventional method, and the intrinsic viscosity (in orthochlorophenol, 35 ° C.) of the polyester is 0.45 or more, because the mechanical properties such as high rigidity of the film are improved. preferable.

  Examples of the polyester include inorganic fine particles such as silicon oxide, aluminum oxide, magnesium oxide, calcium carbonate, kaolin, talc, titanium oxide, and barium sulfate, crosslinked silicone resin, crosslinked polystyrene resin, crosslinked acrylic resin, urea resin, and melamine resin. Organic fine particles made of a heat-resistant polymer can be contained. In addition, other resins such as polyethylene, polypropylene, ethylene / propylene copolymer, olefinic ionomer, stabilizers, antioxidants, ultraviolet absorbers, fluorescent brighteners, and the like may be included as necessary. In addition, since the surface protection film of this invention is requested | required that transparency is high depending on a use, it is preferable to select the usage-amount suitably for the said various additives according to the required characteristic of various uses.

  The polyester film in the present invention can be produced by any conventionally known method. For example, for a biaxially stretched polyester film, after drying the polyester, it is melted in an extruder, extruded from a die (eg, T-die, I-die, etc.) onto a rotating cooling drum, and rapidly cooled to produce an unstretched film. Then, the unstretched film can be produced by stretching in the longitudinal direction and the transverse direction, and heat-setting as necessary. The thickness of the polyester film is preferably 5 to 250 μm.

The polyester film of the present invention has a primer layer formed from a coating solution containing a corona treatment or a primer layer (an easy-adhesive coating film), particularly a silane coupling agent, on one surface, that is, a surface on which a surface layer is provided. It is preferable from the viewpoint of improving the water resistance of the surface layer. Examples of the component for forming the primer layer include a silane coupling agent, alkaline inorganic fine particles, an acid for adjusting pH, and a surfactant. Silane coupling agent is a compound represented by the general formula YRSiX _3. Here, Y is an organic functional group such as a vinyl group, an epoxy group, an amino group or a mercapto group, R is an alkylene group such as methylene, ethylene or propylene, and X is a hydrolyzable group such as a methoxy group or an ethoxy group or an alkyl group. . Specific examples of the compound include vinyltriethoxysilane, vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N- (β-aminoethyl) -γ-amino. Examples thereof include propyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, and γ-mercaptopropyltrimethoxysilane. Of these, preferable silane coupling agents include those having water solubility or water dispersibility, such as γ-glycidoxypropyltrimethoxysilane.

  Examples of the alkaline inorganic fine particles for forming the primer layer together with such a silane coupling agent include iron oxide sol, alumina sol, tin oxide sol, zirconium oxide sol, silica sol and the like, and alumina sol and silica sol are particularly preferable. Among these, silica sol is preferable from the viewpoint of promoting the initial reactivity (dimerization, trimerization, etc.) of the silane coupling agent. The alkaline inorganic fine particles preferably have a small particle size with a large surface area, and those having an average particle size of 1 to 150 nm, more preferably 2 to 100 nm, and particularly 3 to 50 nm are preferable. When the average particle diameter is larger than 150 nm, the surface area becomes too small, the reaction promoting action of the silane coupling agent is lowered, and the surface of the primer layer becomes rough, which is not preferable. On the other hand, if the average particle size is smaller than 1 nm, the surface area is too large, and the reaction control of the silane coupling agent becomes difficult, which is not preferable. The amount of the alkaline inorganic fine particles is preferably 1 to 50% by weight, more preferably 2 to 20% by weight, based on the amount of the silane coupling agent. If this amount is less than 1% by weight, the crosslinking reaction does not proceed. On the other hand, if it exceeds 50% by weight, the coating solution lacks stability, for example, precipitation occurs in the coating solution in a short time after the addition of inorganic fine particles. It is not preferable.

  The pH of the primer coating solution containing a silane coupling agent and alkaline inorganic fine particles, particularly an aqueous coating solution, is adjusted to 4.0 to 7.0, preferably 5.0 to 6.7. If the pH is less than 4.0, the catalytic activity of the inorganic fine particles is lost. On the other hand, if it exceeds 7.0, the coating liquid becomes unstable and precipitation occurs, which is not preferable. As the acid for adjusting the pH, inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid and organic acids such as oxalic acid, formic acid, citric acid and acetic acid are used, and organic acids are particularly preferable.

  A necessary amount of a surfactant such as an anionic surfactant, a cationic surfactant, or a nonionic surfactant can be added to such a coating solution, particularly an aqueous solution. As such surfactants, those that can lower the surface tension of the coating solution to 0.5 N / m or less, preferably 0.4 N / m or less, and promote wettability to the polyester film are preferable. Oxyethylene alkyl phenyl ether, polyoxyethylene-fatty acid ester sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate, alkyl sulfosuccinate, quaternary imonium chloride, alkylamine hydrochloride, etc. Can give. Furthermore, other additives such as an antistatic agent, an ultraviolet absorber, a pigment, an organic filler, a lubricant, and an antiblocking agent can be mixed within a range not losing the effect of the present invention.

  The primer layer can be formed by applying the above coating solution on one side of a polyester film by a normal primer coating method, followed by drying and thermal crosslinking. For example, it may be formed by applying a biaxially stretched heat-fixed polyester film and then applying the polyester film. Application in the film production process is preferred. In particular, it is preferable to apply it as an aqueous coating liquid on one side (side on which the surface layer is provided) of the polyester film before completion of crystal orientation in this step. Here, the polyester film before the crystal orientation is completed is an unstretched film obtained by heat-melting polyester to form a film as it is; A uniaxially stretched film oriented in either direction, or a biaxially stretched film that has been stretched and oriented at low magnification in both the machine direction and the transverse direction (finally oriented and crystallized by redrawing in the machine direction or transverse direction) Including a biaxially stretched film before completion of the process. In a normal process, it is preferably applied after uniaxial stretching in the longitudinal direction. The polyester film before the completion of crystal orientation, to which the coating solution has been applied, is dried and guided to processes such as stretching and heat setting. For example, a longitudinally uniaxially stretched polyester film coated with a coating solution is guided to a stenter and laterally stretched and heat-set. During this time, the coating solution is dried and thermally crosslinked. Such processing can be performed under conditions accumulated in the industry. As preferable conditions, for example, the drying conditions are 90 to 130 ° C. × 2 to 10 seconds, the stretching temperature is 90 to 130 ° C. for polyethylene terephthalate, 120 to 180 ° C. for polyethylene naphthalate (PEN), and the draw ratio. Is 3 to 5 times in the longitudinal direction, 3 to 5 times in the transverse direction, and 1 to 3 times in the longitudinal direction if necessary. When heat-fixed, it is 180 to 240 ° C. for polyethylene terephthalate, and 220 to 240 for PEN. C. and the heat setting time are 2 to 20 seconds. Thus, a polyester film having a primer layer having a thickness of 20 to 1000 nm is obtained.

  As a coating method, any known method can be applied. For example, kiss coating method, bar coating method, die coating method, reverse coating method, offset gravure coating method, myer bar coating method, gravure coating method, roll brush method, spray coating method, air knife coating method, immersion method, curtain coating method These may be applied alone or in combination, and a method using a reverse roll coater is preferably exemplified.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, each evaluation in an Example followed the following method.
(1) Surface Specific Resistivity Using a resistivity meter manufactured by Advantest Corporation, the surface specific resistivity after 1 minute was measured at an applied voltage of 100 V in an atmosphere at a measurement temperature of 23 ° C. and a measurement humidity of 65% RH. The surface resistivity is preferably 1 × 10 ¹² Ω / □ or less.
(2) Water resistance After immersing in ion-exchanged water for 1 minute, a weight is placed on a becot containing ion-exchanged water so as to be 500 g / cm ^2, and rubbed in one direction 5 times to visually check the degree of surface layer shedding. Observe and judge according to the following criteria.
(Double-circle): There is no change even if the frequency | count of rubbing is 10 times.
○: No change or thin scratches remain.
Δ: Discolored slightly after rubbing.
X: The background of the polyester film appears completely in 50% or more of the rubbed portion. Or it becomes cloudy white.
(3) Contact angle of water The contact angle 10 seconds after dropping water was measured using an Elma contact angle measurement image analyzer.
(4) Peel strength of the surface layer Acrylic adhesive tape (Nitto 31B) is bonded to the surface layer side of the surface protective film with a rubber roll, pressed with a 5 kg pressure roller and left for 1 hour, and then the pressure-sensitive adhesive layer side of the surface protective film The release film laminated on was peeled and removed, the pressure-sensitive adhesive surface was fixed to an aluminum support plate with a double-sided tape, the acrylic pressure-sensitive adhesive tape was folded back at 180 °, and the peel strength was measured with a tensile tester. In addition, the preferable range of peeling strength is 5 N / 25mm or more. If the peel strength is less than 5 N / 25 mm, the adhesive tape that peels off the surface protective film is poorly adhered, and the surface protective film cannot be peeled off.

[Examples 1 to 3 and Comparative Examples 1 to 5]
The surface layer composition 1 shown in Table 1 is applied to one side of a polyester film having a wet tension of 54 mN / m or more as measured with a wet tension test mixture on both sides of a biaxially oriented polyester film having a thickness of 38 μm. Apply a coating solution prepared by adjusting -8 to a concentration of 2% by weight at a rate of 4 g / m ² using a reverse roll coater, followed by drying for 1 minute at a dryer zone of 140 ° C. Thus, a polyester film having a surface layer was obtained. Next, as the acrylic adhesive, 2-ethylhexyl acrylate (main monomer), n-butyl acrylate (main monomer), vinyl acetate (comonomer), and 2-hydroxyethyl methacrylate (functional group-containing monomer) are 5: 2: 2. A composition mixed at a weight ratio of 1: 1 and an additive comprising an epoxy-modified stearyl acrylate were added so that the latter additive was 0.5 part by weight with respect to 10 parts by weight of the former composition, and ethyl acetate was added. The solution polymerization was carried out using azobisisobutyronitrile as a reaction catalyst under the above solvent. The weight average molecular weight of the obtained polymer for pressure-sensitive adhesives was about 350,000. After adding a TDI-based isocyanate crosslinking agent (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) to this adhesive polymer in a solid content ratio of 100 parts by weight of the adhesive polymer in a ratio of 7 parts by weight of the crosslinking agent, 25 μm polyester It is applied to the side of the release layer of the release film having a silicone release layer on one side of the film so that the thickness after drying is 15 μm, dried at 100 ° C. for 2 minutes, and then opposite to the polyester film provided with the surface layer. The surface and the pressure-sensitive adhesive layer surface were bonded together and subjected to aging treatment at 45 ° C. for 1 week to obtain surface protective films of Examples 1 to 3 and Comparative Examples 1 to 5. Table 2 shows the physical properties of the obtained surface protective film.

[Example 4]
A surface protective film was prepared under the same conditions as in Example 2 except that the following coating solution was applied as a primer on one side of the film after the longitudinal stretching to a thickness of 40 nm after dry transverse stretching. Table 2 shows the physical properties of the obtained surface protective film.

Coating solution used for primer layer: 83 parts by weight of silane coupling agent (γ-glycidpropyltrimethoxysilane), 2 parts by weight of inorganic fine particles (silica sol having an average particle size of 6 nm, 20% dispersion pH 9.5), nonionic interface An aqueous coating solution containing 15 parts by weight of an activator (polyoxyethylene nonylphenyl ether) and adjusted to pH 6.3 with citric acid

Plus Coat Z450 Kyodo Chemical Industry Co., Ltd. Nicazole RX-1014 Nippon Carbide Industry Co., Ltd. Bytron P Starc Co., Ltd. Resam M643 Chukyo Oil Co., Ltd. DMSO Wako Pure Chemical Industries, Ltd. Emulgen 420 Kao Co., Ltd.

  As is apparent from Table 2, the surface protective film of the present invention is excellent in the surface resistivity and water resistance of the surface layer, so that it is a process for producing optical sheets such as polarizing plates, retardation plates and viewing angle widening films. It can also be seen that it is suitable as a surface protective film in a panel manufacturing process using these optical sheets.

  The surface protective film of the present invention described above is used in, for example, an optical sheet manufacturing process such as a polarizing plate, a phase difference plate, and a viewing angle widening film, or in a panel manufacturing process using these optical sheets. In this case, charging due to friction or peeling can be suppressed on the surface of the optical sheet in each process, and even after the water washing process, the water resistance is good, so that defect inspection can be performed with high accuracy.

Claims (7)

A surface protective film having a surface layer formed from a coating liquid having the following composition on one side of a polyester film and an adhesive layer on the other side, wherein the surface layer is water-soluble or water-miscible with a boiling point of 150 ° C. or higher. A surface protective film formed using an aqueous coating solution containing 0.2 to 3.0% by weight of a liquid based on the total weight of the solvent in the coating solution.
Composition of coating liquid (A) a polyester resin, an acrylic resin, at least one resin component selected from the group of acrylic modified polyester resin and urethane resin (component excluding the solvent agent) active ingredient in the coating solution by weight 55 to 89% by weight,
(B) the following general formula consisting of polythiophene polythiophene-based conductive polymer units as the main repeating unit represented by the antistatic agent: 7-40 (the ingredients except the solvent agent) by weight active ingredient in the coating solution as a reference weight%,

(In the formula, R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms, or together, the alkylene group having 1 to 12 carbon atoms which may be optionally substituted together) Represents
(C) a polyvinyl alcohol or polyethyleneimine chlorinated alkyloyl or alkyl isocyanate composed of a copolymer which is a long chain alkylating antifouling agent (component excluding the solvent agent) active ingredient in the coating liquid 4, based on the weight 9% by weight The surface protective film according to claim 1, wherein the surface layer has a surface resistivity of 1 × 10 ⁵ to 1 × 10 ¹² Ω / □.   The surface protective film according to claim 1 or 2, wherein the water contact angle of the surface layer is 70 ° to 100 °.   The surface protection film according to any one of claims 1 to 3, wherein the peel strength of the surface layer with respect to the acrylic adhesive tape is 2 to 6 N / 25 mm or more.   The surface protection film of any one of Claims 1-4 which has a primer layer formed from the coating liquid containing a silane coupling agent as a main component between a polyester film and a surface layer.   The surface protective film according to claim 1, wherein the pressure-sensitive adhesive layer has an adhesive strength of 0.03 to 0.50 N / 25 mm.   The surface protective film of any one of Claims 1-6 used for the surface protection of a polarizing plate, a phase difference plate, or a viewing angle expansion film.